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Hacking body with light could speed jet lag recovery

By Ewen Callaway

Every regular flier has their favourite trick for kicking jet leg, from naps to caffeine. Now a computer program could take much of the guesswork out of these countermeasures, recommending precisely timed light treatments to reset the body’s circadian clock.

The circadian clock acts like a pendulum. Over the space of 24 hours or so, the pendulum swings back and forth to complete a cycle. After an abrupt time change this cycle ends up out-of-whack relative to the new time zone. The circadian clock relies on light to recalibrate itself each day. But a poorly timed nap or cup of coffee has the potential to make things worse by pushing the pendulum further out of sync.

To determine when and how to nudge the circadian clock into a new time zone, Dennis Dean and Elizabeth KIerman at Brigham and Women’s Hospital in Boston developed a series of mathematical equations connecting circadian cycle, sleep schedules, mental performance, and light exposure.

Light relief

Other researchers have previously modelled the circadian clock using maths, but no one had approached the task with the goal of hacking the clock with extra light. “Because we have a model that has light stimuli as an input to the circadian system, we can use the model to develop a countermeasure using light,” Klerman explains.

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Their model also used data collected from hundreds of people involved in sleep studies, which sometimes last more than two months.

Such experiments take place in a specially designed hospital unit staffed 24 hours a day, 350 days per year. Researchers record all vital signs, while tinkering with their sleep schedules and testing their performance on a series of mental tasks. None of the rooms have windows and clocks and calendars are forbidden. “We want them to tell us how they feel without knowing what day it is,” Klerman says.

Fantasy flight

To demonstrate their model, the researchers simulated the effects of their targeted light therapy for people on an imaginary trip from New York to Hong Kong – a 12-hour time difference.

Without light therapy, the traveller’s circadian clock slowly inched back into sync with the new time zone, but was still off schedule after 12 days. As a result, the traveller is in peak mental form for only a few waking hours a day. However, a traveller who received a six-hour light session at progressively later times each day was back on schedule after just eight days. They were also alert for most of the day.

Dean and Klerman also found that their model was able to predict the circadian responses of laboratory volunteers that had experienced changes mimicking jet lag.

A beta version of the computer program is already available for download. Klerman and Dean hope to license their program to a software company who will create a more user-friendly version. “The whole idea with this program was to be able to just click on one button,” says Dean.

In practice, users will need to know the approximate length of their own circadian clocks, as well as the brightness of the light they’re using to jog their clocks, Klerman says.